The purpose of this application is to request continued support for an already established facility devoted to the experimental study of neurobiological problems. The laboratory serves two main functions. First, it offers access to the marine fauna which inhabits the littoral waters of Puerto Rico, as well as to the many scientifically interesting invertebrate species found in the rain forest of this island. Second, it provides, to local and visiting scientists alike, the necessary facilities to allow projects to be conducted in the areas of morphology, including ultrastructure, electrophysiology, toxicology and pharmacology of the nervous system and in general of excitable tissues and cells. The nature and mechanism of action of toxins and other biologically active compounds, receive also particular attention. BIBLIOGRAPHIC REFERENCES: "Induction of excitability, rhythmicity and bursting in an electrically stable membrane following chemical interaction with sulfhydryl and disulfide groups at the cell surface membrane" (C. Zuazaga de Ortiz and J. del Castillo). Invited paper to the Colloquium on "Abnormal Neuronal Discharges" Monaco, July 1977, Raven Press in press. "Influence of succinic anhydride on the decay of endplate currents evoked by high frequency stimulation" (J. del Castillo and G. Escalona de Motta) Abstract. Annual Meeting, Society for Neuroscience, 1977, in press.